A. Field of the Invention
This invention relates to hypoallergenic cellulosic fibers having increased absorbency for water and physiological liquids and a method for their preparation.
B. Description of the Prior Art
Cellulosic fibers, because of their absorbency, have been found particularly useful in the production of nonwoven articles that require a high absorbency, such as diapers, tampons, sanitary napkins, medical sponges, soil mulches, wiping cloths, and the like. Each of these applications requires a material having a high capacity for absorbing and retaining water and other aqueous fluids, particularly body fluids. Cellulosic fibers have found wide use in these and similar applications because of the hydrophilic nature of the cellulose molecule and the fibrous structure which contributes integrity, form, shape, wicking ability, and liquid retention to a nonwoven material.
Various procedures have been proposed for increasing the absorbency of cellulosic fibers. For instance, the physical properties of cellulosic fibers, especially rayon fibers, have been altered by incorporating into the rayon a substance capable of increasing the fluid-holding capacity of the rayon, i.e., hydrophilic organic polymers or copolymers such as copolymers of acrylic acid and methacrylic acid or their alkali metal or ammonium salts. Representative of such a procedure is disclosed in U.S. Pat. No. 4,240,937, which is hereby incorporated by reference. These fibers are known as alloy rayon fibers, as the fibers are formed from a uniform mixture of an aqueous alkaline cellulose xanthate solution and the substance capable of increasing the fluid holding capacity of the rayon. A problem associated with this procedure is that undesirable losses and interaction can occur between the substance and the aqueous acidic spin bath into which the fluid containing cellulose and substance are regenerated to form the alloy rayon fibers. This problem can become particularly acute as the losses can floculate or agglomerate in the spin bath system.
Another procedure for increasing the absorbency of cellulosic fibers involves coating the surface of the fibers with a hydrophilic chemical, polymer, or gel in order to enhance the swelling of the cellulosic fibers. Representative of such a procedure is disclosed in U.S. Pat. No. 4,128,692, which is hereby incorporated by reference. A problem associated with this procedure is that many times the cellulosic fibers coated with the chemicals, polymer, or gel become glued, matted, or hard, which results in fibers that are difficult to process.
Whether utilizing chemicals, polymers, or gels to coat the cellulosic fibers or to produce alloy fibers, their use results in additional expenses. Also, their use can result in an allergic response to persons coming into contact with the cellulosic fibers containing the chemicals, polymers, or gels. Thus, there are certain advantages in using procedures which avoid the use of certain chemicals, etc.
One such proposed procedure for increasing the absorbency of cellulosic fibers without the use of these chemicals, etc., involves heating cellulosic fibers in a water bath at temperatures in the range of from 95.degree. C. to 100.degree. C. for periods ranging from one to sixty minutes. This procedure is disclosed in U.S. Pat. No. 4,575,376, which is hereby incorporated by reference. Although this procedure has been somewhat successful, certain problems remain. For instance, for many applications, it is desirable that the absorbency of the cellulosic fiber be increased to a greater degree than resulting cellulosic fiber treated in accordance with U.S. Pat. No. 4,575,376. In addition, to achieve the desired absorbency of the cellulosic fibers for certain applications, it is sometimes necessary that the fibers be treated in the hot water bath for unacceptably long periods of time. In many commercial plant operating conditions, this amount of time results in unacceptable additional expenses for preparing cellulosic fibers having the desired amount of absorbency.
Thus, there is a need for a method for increasing the absorbency of cellulosic fibers which involves only modest cost and results in hypoallergenic cellulosic fibers having the increased absorbency.